Aircraft gas turbine engines operate on fuel which is basically kerosene, which is much less volatile than gasoline. However, it has been found that in the event of a crash the fuel is subjected to a shock which causes it to spray out of the tank in a highly flammable mist; this is the cause of most of the post-crash fires, which are the cause of more deaths and injuries than the crashes themselves. Likewise, if the tank is ruptured in flight the fuel gets caught in the airstream and is broken up into the same highly flammable mist.
To combat this misting tendency, certain additives have been discovered which can be added to the fuel to reduce its mist formation under these conditions; these are known as "anti-misting" additives. See U.S. Pat. No. 3,996,023 for a discussion of anti-misting polymer additives. It has been found that these same polymers, when dissolved in fluids, reduce the friction generated when the mixture is flowing in a pipline or over a surface; see U.S. Pat. No. 3,692,676.
Although the desirable properties of these modified fluids are well known, a good test has not yet been devised which will measure these properties or which will allow the prediction of these properties when an unknown additive is tested for the first time. The prior art shows two tests, neither of which is very exact or which produces easily quantifiable results. The first of these tests is that described in U.S. Pat. No. 3,996,023 and comprises dropping a thin stream of fluid into the center of a hollow cylinder whose walls are lined with absorbent paper; the drops of fluid which splash onto the paper are then counted, and the polymer additive concentration is increased until no drops splash onto the paper. The second test is described in U.S. Pat. No. 3,998,605 and is essentially a version of the "slump" test that is used to determine the water content of freshly-mixed concrete. In this test the liquid under test is placed in an open ended cylinder 20 cm in diameter and 20 cm high and allowed to stand for a short time. The cylinder is then lifted up, and the behavior of the liquid is observed. If the fluid spreads out to a thickness of less than a millimeter, the concentration of additive is too low; if it spreads out to a thickness of 10 cm or more, the concentration is too high for present fuel systems (i.e., it would not flow out of the fuel tanks, special pumps would be required, etc.). Under this test the optimum thickness is 0.5-5 cm.
The present invention is a test which is clean, easily performed, and produces useful results.